Kreen is a very different chemistry from Seafoam and MMO.
Seafoam and MMO are primarily Pale oil and Naphtha based.
Seafoam was developed in the 1930's by a fisherman for his marine outboard with water issues. Hence the name and the additional 20% IPA for water/gas issues. During a "seafoaming" these chemicals resemble a white cloud as they are combusted. This white cloud should not be confused with carbon, which is brown. 20% IPA in the tank will feel like 94 octane for the balance of the tankful.
MMO was developed to assist with issues experienced in WW2 airplane engines. MMO has a wintergreen red dye to distinguish its use.
Kreen was developed to deal with problems gas and diesel engines had in the 1930's like varnish, sludge and carbon buildup.
All are old chemistry. Each had a different purpose. Somehow all 3 ended up being marketed as motor tonics. Having used the 3 over the years I am not recommending any of them unless your trying to solve a problem. Standard use of a good synthetic like M1 or PU with an occasional bottle of Techron fuel system cleaner should be enough. Kreen is much stronger than MMO and Seafoam, not too strong that it requires a drain directly after use. The emulsification and suspension is quite good, no fear of large chunks falling into the oil return, sump screen, etc. Does a decent job on varnish. Has a strange side effect where it evaporates by 50%, and that evaporation causes the chemicals to get up in the PVC, back to the TB/IAC, clean anywhere the oil vents to.
I haven't taken any pictures but if you guys want I can show some filler hole results. this is a 99 intrepid the lady let run out of oil, didn't change the oil for 2+ years. Right now it has 3.5qts of my favorite cleaning oil, Mobil 1 High Mileage. I put that in to test the car prior to Kreen, see how stable the engine is after driving so long without oil/no oil change.